Gastric MALT lymphoma

Biopsy of a gastric MALT lymphoma showing a dense cellular infiltrate showing virtually complete obliteration of the normal architecture (upper panel). At high power (lower panel) the infiltrate is composed of atypical lymphoid cells that are infiltrating and partially destroying the glands (arrows), referred to as "lymphoepithelial lesions". Immunohistochemical studies demonstrated that the lymphoid cells were CD20 positive and CD5 and 10 negative. This findings supports the diagnosis of mucosa-associated lymphoma (MALT). The other major consideration in the differential diagnosis is poorly differentiated carcinoma, which would be negative with the CD makers but positive with stains for cytokeratins. Special stainings revealed the presence of Helicobacter pylori.